What to do about a neighbor who looked through your mail?

This suggestion by ND¢ stood out to me:

... it also may help to give him a way out.

"Hi Jim. My mother-in-law tells me that she saw you opening our mailbox while walking your dog last Wednesday about 11:00 am. Were you returning some of our mail delivered to you by mistake?"

In other words, it helps to be willfully vague when making an accusation. As a designer at a video game company, there were so many times when you'd bumped up against someone else's code, and have to point out someone's mistakes. As a result, we used lots of indirect comments like, "What's on this character's back?" "How did fixing that bug go?" "Do you want to me to tell quality assurance to double-check that?" These comments are, in some way, borderline passive-aggressive, when they're actually necessary to smooth out communication.

Our design department was also notorious for joking around at the office. I wonder if we'd be at each other's throats otherwise.

It always helps to leave room for a charitable interpretation. I asked my friend in college, who I wanted to accuse of trash-talking, "You know, you were talking about our friend the other day. I was wondering if you could walk me through that. Because an uncharitable interpretation is that you were talking behind his back." He quickly back-pedaled, told me that him and our friend go way back, always with ups and downs, and that his criticism was more of a familial critique. That put me at ease, and I also feel I got through to him.